Quick Facts

Quick facts

  • Originally from Southern Europe and Western Asia, Soldier Thistle (Picnomon acarna) is a prickly, upright, annual thistle growing up to 100 cm tall.
  • It is found in western parts of Victoria and the south-eastern parts of South Australia.
  • Soldier Thistle competes with cereal crops and interferes with harvesting by clogging machinery.
  • It invades pastures and its sharp spines can injure sheep, dogs and humans and decrease suitable grazing areas for stock.
  • It can be controlled by hand grubbing, cultivating, mowing, slashing or treating with herbicides before the flowering head develops.

What Does It Look Like?

What is it?

Soldier Thistle (Picnomon acarna) is a prickly, upright, annual thistle usually growing to 500-750 mm tall, but occasionally reaching 1 metre in height growing in semi-arid to sub-humid areas with rainfall of 300-600 mm. It forms a basal rosette (cluster) of leaves during the early stages of growth. The long thin spiny rosette leaves are oblanceolate (lance shaped, about 4 times as long as broad, broadest in the upper half, tapering to a narrow base) and grow to 300 mm long and 30 mm wide, slightly lobed, with many teeth with many distinct short yellow spines, covered in cobwebbed white hairs. The stems and leaves are densely covered in white hairs that give them a cobwebby or woolly appearance. The stems are many branched and have spiny 'wings' that extend downwards from the base of the leaves. The stem-leaves are mostly smaller 40-100 mm long and 4-20 mm wide, lanceolate (about 4 times as long as broad, broadest in the lower half and tapering to the tip ), deeply lobed, with long yellow coloured spines on their teeth or lobes, cobwebby, and prominently veined.

The pink or purple flower-heads are almost stalkless (sessile), cylindrical (20-40 mm x 10 mm in size), and borne singly or in small groups. They consist of numerous pink or purple coloured 'florets' (small individual flowers) surrounded by several layers of bracts (modified leaves) 20-30 mm long, that are tipped with sharp, multi-forked, yellow spines.

The fruits or 'seeds' (cypselas) are 4-6 mm long, brown to black in colour and topped with a ring (pappus) of feathery white bristles (10-20 mm long) (Parson & Cuthbertson 2001; Navie 2004).

For further information and assistance with identification of Soldier Thistle, contact the herbarium in your state or territory.

Flower colour

Purple or Pink

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

Soldier Thistle (Picnomon acarna) is a weed of roadsides, waste areas, channel banks, crops and pastures in temperate, semi-arid and sub-humid environments. It grows on dry sandy or stony soils in areas with 300 to 600 mm of rainfall and a relatively long growing season (Parsons & Cuthbertson 2001; Navie 2004).

Are there similar species?

Soldier Thistle (Picnomon acarna) is relatively similar to Star Thistle (Centaurea calcitrapa), Spotted Knapweed (Centaurea maculosa), Black Knapweed (Centaurea nigra) and Creeping Knapweed (Rhaponticum repens) [as Acroptilon repens]. These species can be distinguished by the following differences:

  • Soldier Thistle has spiny, winged, stems and a covering of short white hairs on the undersides of its toothed or slightly lobed, spiny, leaves. Its pinkish or purplish flower-heads are enclosed in several rows of spine-tipped bracts.
  • Star Thistle has spineless stems and a covering of short hairs on the undersides of its lobed or deeply-divided, spineless leaves. Its purplish flower-heads are enclosed in several rows of spine-tipped bracts.
  • Black Knapweed has spineless stems and a sparse covering of rough hairs on the undersides of its mostly entire (without teeth or lobes), spineless leaves. Its purplish flower-heads are enclosed in several rows of spineless bracts.
  • Spotted Knapweed has spineless stems and a sparse covering of short hairs on the undersides of its entire, lobed or deeply-divided, spineless leaves. Its purplish flower-heads are enclosed in several rows of spineless bracts.
  • Creeping Knapweed has spineless stems and a covering of short hairs on the undersides of its entire, toothed or deeply-divided, spineless, leaves. Its purplish flower-heads are enclosed in several rows of spineless bracts (Navie 2004).

Why Is It A Weed?

What are its impacts?

Soldier Thistle (Picnomon acarna) is mostly a weed of agriculture, but also invades roadsides, channel banks and other disturbed areas. The sharp spines can injure animals and people.

Agriculture: Invades both cropping and pastures. In pastures sheep and cattle avoid grazing it because it is so spiny, and the available infested areas are reduced, while Soldier Thistle spreads further. When well established, Soldier Thistle competes with cereal crops and interferes with harvesting by clogging machinery. Its sharp spines can injure sheep, dogs and humans and decrease grazing areas by excluding stock ( Agriculture Victoria 2021; Parsons & Cuthbertson 2001).

Native ecosystems: May invade degraded and disturbed areas, especially on the edges of native vegetation.

Urban areas: Can invade roadsides and abandoned and disturbed sites. Its sharp spines can injure dogs and humans.

How does it spread?

Soldier Thistle (Picnomon acarna) disperses via seeds, with seeds or as whole plants which readily break off at the base and are dispersed by wind, sheading seed. The sharp spines of seeds become attached to wool and hides and are dispersed in that way or seeds are spread through the movement of vehicles, mud and water (Parsons & Cuthbertson 2001).

What is its history in Australia?

Soldier Thistle (Picnomon acarna) was a serious problem in Victorian Mallee and Wimmera districts in the 1930s and 1940s, but effective control measures and increased soil fertility has lessened its impact because other species are more competitive in more fertile soils (Parsons & Cuthbertson 2001). There are early herbarium records for Soldier Thistle at Sellicks Hill, South Australia, from 1908 (AVH 2021; eFlora 2021).

How To Manage It?

Best practice management

Soldier Thistle (Picnomon acarna) can be controlled by herbicides, and non-mechanical means like physical, and mechanical methods. The method used depends on the age of plants, size of the infestation, and where they are growing.

Chemical control: Herbicide is effective at the rosette stage, but the plant becomes harder to kill as it gets older. Spraying of older plants should be discouraged as it is not entirely effective and promotes resistance to some herbicides (Parsons & Cuthbertson 2001).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au.

Non-chemical control: Physical control:  For sparse populations, the most effective means of control is hand grubbing.

Mechanical control: Larger infestations of mature plants can be controlled by cultivating, mowing or slashing before flowering.

Competition and management: Increased fertility of soil excludes the weed because other species are more competitive in more fertile soils. As with other weedy thistles, maintaining healthy dense pastures helps exclude Soldier Thistle, while cultivation and herbicide application in cropping will help mange the weed.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Soldier Thistle (Picnomon acarna) germinate after autumn rains and small rosettes slowly develop over winter. Growth accelerates as the weather warms up with flowering stems being produced by late spring. Flowering occurs in early summer and plants die off by late summer or autumn (Parson & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

SA, VIC

What areas within states and territories is it found?

Soldier Thistle (Picnomon acarna) is found in the western parts of Victoria, west of Melbourne and Echuca and south and west of Mildura (AVH 2021).

In South Australia it is found in south-eastern parts, around Adelaide, the Mid-north and several outlier collections from Yorke Peninsula, Kangaroo Island,  Riverlands, the Coorong, and the Upper South-East (Navie 2004; AVH 2021).

Where does it originate?

Soldier Thistle (Picnomon acarna)  originated in southern Europe and south-western Asia (Navie 2004).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

VIC

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Picnomon acarna

Other scientific names (synonyms)?

  • Carduus acarna L.
  • Carlina acarna (L.) M.Bieb.
  • Cirsium acarna (L.) Moench
  • Cnicus acarna (L.) L.

Does it have other known common name(s)?

Yellow-plumed Thistle, Yellow Plumed Thistle

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